GROWING THUNBERGIA

Thunbergia data, black-eyed Susan, is a delightful South African climber, easily grown as an annual from seed sown early in the year. It starts flowering in the young seedling stage and continues to bloom with the utmost freedom until autumn.

The plant can be grown easily from seed sown under window-sill conditions. A packet of seeds usually gives a batch of plants with variously coloured flowers, including pale cream, pale orange, and vivid orange, with or without a jet-black eye. It is usually best to discard all those without the eye, and even all those without the best orange colour. It is the plants with the vivid orange, contrasting with a black eye, that are the most striking. Fortunately, this colouring usually predominates a batch. These plants are also the ones mostly sold as small pot plants by florists in late spring or early summer.

The plants can be grown up a fan of bamboo canes, or one of the plastic trellis-type supports sold for the smaller houseplant climbers, or put in hanging-baskets. Although the tendency is for the plant to climb, it can be persuaded to trail. Usually, at least three plants will be needed for a basket, and it is a help to fix the stems down to the basket sides at first as they grow. Pieces of bent wire can be used for this.

As a climber, the plant’s height varies with growing conditions and may reach about 1m (3 ft) or more with average treatment, although far greater heights have been reported. Thunbergia grows easily in any of the usual potting composts. It will grow well in bright positions, as well as slight shade, but too much light tends to bleach the flowers and cause them to pass over more quickly. If possible, remove all faded flowers and the seed pods as promptly as possible to encourage continuous flowering.

Keep the plants well watered throughout summer and maintain moderate humidity. If possible, spray the plants with a mist of water from time to time. especially under foliage. Try to provide a minimum temperature of 10 deg C (50 deg F). Unfortunately, this species is extremely prone to attack by red spider mites, and once an infestation has taken place it becomes very difficult to control the pest, which may also spread to other house-plants. Watch for any sign of yellowing foliage and inspect it through a powerful lens from time to time to see if the tiny spider-like mites, or their minute whitish round eggs, can be seen. Apart from this

specific pest, the plants are rarely troubled by others, or by diseases. At the end of the year, after flowering, the plants can be discarded.

Three other species may make interesting houseplants in certain circumstances. The most useful is probably T. gregorii, often confused with T. gibsonii. Although this is a perennial it can be grown as an annual in much the same way as T. ulaltt. However, the plant is more vigorous and has much larger orange flowers – about 4cm (14in) across – without an eye. It given a free run it will climb to a considerable height and is useful for stair-wells, porches or conservatories. provided the winter minimum can be maintained. If the plant is kept as a perennial it should be moved on to larger pots and at least a 20cm size will be needed. T. grandiflora, an Indian species, is an even more vigorous grower, but is different in having even larger purple-blue flowers. It can be kept to a convenient size by drastic cutting back and pruning. but this does tend to inhibit flowering. This species ultimately needs a large pot. It makes an impressive conservatory or garden room plant, and is also suitable for a glass porch that can be kept warm in winter.

Of very recent introduction as a house-plant, and still needing some trial as a plant suited to this purpose, is the very lovely T. Uiuhfolia, the laurel-leaved thunbergia. The common name of this species is suggested by the shiny, green laurel-like foliage. The flowers are very large and can reach about 13cm (5 in.) across. They are a beautiful lavender-blue, with a contrasting yellow throat, and are freely produced over a long period on mature plants. This species can now be bought as young plants, but these have to be grown on for about three years before they can be expected to flower. However, in the meantime the foliage is quite decorative in itself. This species is native to Malaya, but it is grown in most warm countries and is often a feature. As might be expected, moderate warmth is essential for its success and a winter minimum of about 15 deg C (59 deg F) is recommended. It is best given as much height as possible and grown up canes near a large window. However, this species will tolerate some shade.